Mario is a simple character without a solid personality. When his demeanour is shown, Mario is aggressive and impulsive, sometimes going head-on into things without much meditation. Despite these potential flaws, Mario is a brave and kind-hearted hero.
Luigi is Mario's younger twin brother. Luigi usually joins and accompanies Mario on his adventures, serving as the secondary protagonist (although Mario has been known to go on adventures by himself). Through the years, Mario and Luigi have maintained a brotherly love for each other as shown in games like Luigi's Mansion and the Mario & Luigi series. In addition, the two of them are normally paired together in sports titles and spin-offs and although Luigi has shown to be slightly jealous of Mario at times (as he admits in Paper Mario), he loves his brother very much and looks up to him as a positive role model.
For his part, Mario seems to allow his sibling rivalry to get the best of him when competing directly with Luigi. When Luigi receives a trophy in Mario Power Tennis, Mario slapped Luigi's back and stepped on Luigi's foot intentionally.
Mario realized Wario stole Mario's Castle while he was rescuing Sarasaland including Daisy; but Mario managed to get his castle back. They were also rivals in Mario & Wario with the help of Wanda guiding him. Furthermore, they get along in the Mario Party series